The bead portion of the tire is a particularly critical component by reason of its role as the primary connector, as it were, between the wheel of the vehicle and the ground-contacting tread. The bead is in direct abutting contact with the rim and, in a tubeless tire, is responsible for maintaining the air within the toroidal shell. Centrifugal force tending to throw the tire off the wheel is overcome by the bead. Additionally, of course, and perhaps more important, the forces of acceleration, with respect to the rear wheels, are transmitted to the tire via the abutting contact between the driven wheel rim and the bead. Similarly, in the case of braking or deceleration, the rapid decrease in angular velocity of the wheel is translated to the roller via the tread and the abutting contact between the bead and the rim.
Compounding the problem are the lateral forces to which the bead region is exposed as the vehicle bearing the tire is moved from side-to-side in cornering, frequently simultaneously with acceleration or conversely, deceleration or braking.
Traditionally, bead members have been formed of metal wire which is combined with rubber in an extruding operation, followed by a forming of the bead ring with an appropriate number of winds of the metal wire and a wrapping of the assembly with a friction-coated textile wrap, otherwise known as bead stock.
Recently, glass fibers have been suggested and employed in the manufacture of bead members. For example, U.S. Pat. No. 3,612,139 Marzocchi et al.; U.S. Pat. No. 3,473,595 Marzocchi et al; and U.S. Pat. No. 3,237,674 Budd et al. teach using fiberlgass as a tire bead reinforcement. As these references point out that glass cannot be simply substituted for another reinforcing material. The different properties and characteristics of the glass must be considered in the design. Furthermore, the geometry of the placement of the glass within the bead must be considered. It is believed that hoop stiffness is an important characteristic relating to the quality of bead performance in the tire. Hoop stiffness is the ability of the bead to resist deformation from its circular shape. A lack of sufficient hoop stiffness of the bead is believed to have contributed to the pecularities of early glass beads.
It is well known that the geometrical shape of a body, among other things, determines the ability of a body to resist deformation when subject to external forces. It is conventional practice to fabricate a tire using a bead member in a completely green or uncured state. Generally, a tire is a barrel shaped structure when initially fabricated, and is later transformed into its toroidal shape having a "C" shaped cross section. Furthermore, all of the components of the tire are cured at one time as the final step in fabrication. As a result of such deformation and curing, the carcass plys of the tire exert forces upon the bead structure sufficient to deform the bead structure from its original cross-sectional shape. This means that there is relatively little control over the final shape the bead structure will take under such a process. The present invention allows more control over the final cross-sectional shape taken by the bead member in the completed tire. Thereby, controlling or affecting the stiffness of the bead member by means of the geometry or shape of the bead member.